The present invention relates to a single-substrate-heat-processing apparatus and method for performing a reforming process for removing inorganic impurities contained in a thin film formed on a target substrate and for performing a crystallizing process for crystallizing the thin film, and particularly, to a heat processing apparatus and method applied to a metal oxide film deposited by MOCVD (Metal Organic Chemical Vapor Deposition) method.
In the manufacturing process of a semiconductor device, a film forming process and a pattern etching process are repeatedly applied to a semiconductor wafer. The specification for the film forming process becomes severer and severer in recent years in accordance with increases in the density and in the degree of integration of the semiconductor devices. For example, a further a decrease in thickness and a higher insulating properties are required even for a very thin insulating film such as an insulating film included in a capacitor or a gate insulating film.
A silicon oxide film or a silicon nitride film is widely used as such an insulating film. However, a metal oxide film such as a tantalum oxide (Ta.sub.2 O.sub.5) film has come to be used in recent years as an insulating film exhibiting further improved insulating properties. Such a metal oxide film can be formed by an MOCVD method, in which an organometallic compound is gasified for deposition of the metal. The insulating properties of the metal oxide film can be further improved by applying a reforming process to the surface of the metal oxide film after deposition. A reforming processing technique is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2-283022.
A CVD apparatus is used for forming a tantalum oxide film. A raw material gas containing, for example, tantalum alkoxide (Ta(OC.sub.2 H.sub.5).sub.5) is used as a process gas together with O.sub.2 gas. The process pressure is set at about 0.2 to 0.3 Torr, and the process temperature is set at about 250 to 450.degree. C. Under these conditions, the excited species generated by dissociation of the raw material gas perform reactions with the oxygen gas, with the result that an amorphous tantalum oxide film is deposited on a semiconductor wafer.
A reforming apparatus is used for performing the reforming process of the tantalum oxide film after the deposition. The wafer having the tantalum oxide film formed thereon is put under an atmosphere of the atmospheric pressure containing ozone. Ozone is irradiated with ultraviolet rays emitted from a mercury lamp so as to generate active oxygen atoms. The organic impurities having C--C bonds, etc. and contained in the tantalum oxide film are decomposed by the active oxygen atoms so as to be removed from the tantalum oxide film. As a result, the insulating properties of the tantalum oxide film are improved. Incidentally, the reforming process is carried out at a temperature lower than the crystallizing temperature, e.g., at about 425.degree. C., in order to allow the tantalum oxide film to maintain its amorphous state.
Then, the wafer is transferred into a heat processing apparatus for crystallization. The tantalum oxide film is heated within the heat processing apparatus in the presence of O.sub.2 gas to a temperature higher than the crystallizing temperature, e.g., to about 700.degree. C. By this annealing process, the tantalum oxide film is crystallized and the density thereof is increased in the molecule level, with the result that the insulating properties of the tantalum oxide film are further improved.
Jpn. Pat. Appln. KOKAI Publication No. 9-121035 teaches a tantalum oxide film of a two-layer structure. In this prior art, an amorphous first layer is deposited first on a semiconductor wafer, followed by applying a reforming process to the first layer. Then, a second amorphous layer is deposited on the first layer, followed by applying a reforming process to the second layer. Finally, the wafer is subjected to a heat process at a high temperature so as to crystallize both the first and second layers simultaneously. The technique disclosed in this prior art makes it possible to remove effectively the organic impurities in the step of the individual reforming process because each of the first and second layers is sufficiently thin so as to further improve the insulating properties of the tantalum oxide film. However, the number of the process steps and the number of transfer steps are increased in this prior art, leading to a decrease in the through-put. In addition, the facility cost and the manufacturing cost are increased.
Further, Jpn. Pat. Appln. KOKAI Publication No. 10-79377 (U.S. patent application Ser. No. 08/889,590, now U.S. Pat. No. 6,143,081) relating to an invention achieved by the present inventors discloses a cluster-tool-type film forming system in which a deposition apparatus, a reforming apparatus and a heat processing apparatus for crystallization are connected to each other via a common transfer chamber. The cluster-tool-type film forming system permits solving the problem of the through-put, etc. to some extent. However, a further improvement is required.